This invention relates in general to processes for making ceramic capacitors and, more particularly, to a process which requires less precious metal ink and produces thinner electrodes and substrates having electrical properties equal or superior to prior thick capacitors using greater amounts of precious metal.
Conventional multilayer capacitors generally consist of a number of alternate layers of conductive metal electrodes and dielectric layers, all connected in parallel so as to provide an increase in the electrical capacitance for a given area. This structure is generally referred to as a monolithic construction of electrodes and dielectrics or as a monolithic capacitor. The dielectric may be an insulating synthetic resin, a ceramic material or other insulator. A variety of conducting materials, typically metals, may be used in the electrodes. The thinner the electrodes and dielectric substrates can be made, and the more efficient the electrodes, the smaller the capacitor can be made. This size reduction is important in modern, very compact, electronic systems.
Prior capacitors for these applications are generally made by casting a mixture of ceramic particles and resin, in paint like form, onto a plastic film support. This cast dielectric material is dried, resulting in a rough surface due to the particulate nature of the ceramic. The dielectric substrate is then printed by silk screen processes with an ink made up of finely divided precious metal particles in a resin carrier. In order to achieve the necessary conductivity in the electrode, it is necessary to apply sufficient ink to fill the irregularities in the ceramic surface, then apply sufficient additional ink to produce a coating with a minimum thickness over the ceramic high points for the intended application. Typically, a 0.001 inch thick ceramic substrate will exhibit a roughness of approximately 6 to 7K.ANG.. Thus, conventionally, an electrode thickness of about 54 k.ANG. is required to provide the needed conductibility, where about 7 k.ANG. of the precious metal ink will be required to fill the irregularities in the ceramic surface. The metal ink lodged in the roughness of the ceramic surface contributes little, if anything, to the conductivity of the metal electrode. Thus, if there were no roughness only about 47k.ANG. of metal ink would be needed.
Thus, there is a continuing need for improved processes for making metal coated ceramic substrate capacitors for monolithic multilayer capacitor assemblies which have decreased thicknesses and which use a smaller quantity of the expensive precious metal ink.